Re: [Minios-devel] [UNIKRAFT/UNIKRAFT PATCH 1/2] Add two erratums for Cortex-A53

[Julien Grall <julien@xxxxxxx>]

Hi,

Title: s/erratums/errata/

On 15/01/2020 10:58, Santiago Pagani wrote:
> Add two erratums for Cortex-A53:
> - Workaround for Cortex-A53 erratum 835769
> - Workaround for Cortex-A53 erratum 843419
>
> Signed-off-by: Santiago Pagani <santiagopagani@xxxxxxxxx>
> ---
>   arch/arm/arm64/Config.uk   | 16 ++++++++++++++++
>   arch/arm/arm64/Makefile.uk | 10 ++++++++++
>   2 files changed, 26 insertions(+)
>
> diff --git a/arch/arm/arm64/Config.uk b/arch/arm/arm64/Config.uk
> index 8c20e68d..58483b66 100644
> --- a/arch/arm/arm64/Config.uk
> +++ b/arch/arm/arm64/Config.uk
> @@ -54,3 +54,19 @@ config ARM64_ERRATUM_858921
>           This option enables a workaround for Cortex-A73 (r0p0 - r0p2),
>           whose counter may return a wrong value when the counter crosses
>           a 32-bit boundary. The newer Cortex-A73 are not affected.
> +
> +config ARM64_ERRATUM_835769
> +       bool "Workaround for Cortex-A53 erratum 835769"
> +       default y
> +       help
> +         This option enables a workaround for Cortex-A53, which involves
> +         inserting a NOP instruction between memory instructions and
> +         64-bit integer multiply-accumulate instructions.
> +
> +config ARM64_ERRATUM_843419
> +       bool "Workaround for Cortex-A53 erratum 843419"
> +       default y
> +       help
> +         This option enables a workaround for Cortex-A53. This erratum
> +         workaround is made at link time and this will only pass the
> +         corresponding flag to the linker.
> diff --git a/arch/arm/arm64/Makefile.uk b/arch/arm/arm64/Makefile.uk
> index eb73cace..72dbf55c 100644
> --- a/arch/arm/arm64/Makefile.uk
> +++ b/arch/arm/arm64/Makefile.uk
> @@ -32,6 +32,16 @@ CFLAGS-$(call gcc_version_ge,4,9)    += -march=armv8-a 
> -mcpu=cortex-a53 -mtune=cort
>   CXXFLAGS-$(call gcc_version_ge,4,9)   += -march=armv8-a -mcpu=cortex-a53 
> -mtune=cortex-a53
>   endif
>   
> +ifeq ($(CONFIG_ARM64_ERRATUM_835769),y)
> +CFLAGS-$(call gcc_version_ge,4,9)      += -mfix-cortex-a53-835769
> +CXXFLAGS-$(call gcc_version_ge,4,9)    += -mfix-cortex-a53-835769
> +endif
> +
> +ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
> +CFLAGS-$(call gcc_version_ge,4,9)      += -mfix-cortex-a53-843419
> +CXXFLAGS-$(call gcc_version_ge,4,9)    += -mfix-cortex-a53-843419
> +endif
If I understand correctly, the workaround will only be turned only for 
GCC 4.9 and higher. For older versions, you will silently ignore it.
In other words, a user may not realized the workaround was not used and 
therefore will see weird error later on. So how about requiring 4.9 when 
using the workaround?
> +
>   # GCC support -mcpu=cortex-a57 for arm64 from 4.9
>   ifeq ($(CONFIG_MARCH_ARM64_CORTEXA57),y)
>   $(call error_if_gcc_version_lt,4,9)
Cheers,

--
Julien Grall

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